1. Field of the Invention
A technology disclosed in this description relates to a semiconductor device.
2. Description of Related Art
Japanese Patent Application Publication No. 2012-195339 A (JP 2012-195339 A) discloses a semiconductor device in which a temperature sensing diode and an IGBT are provided in a same semiconductor substrate. It is stated that, in this semiconductor device, it is possible to carry out highly accurate temperature detection in an entire temperature range of rated temperature of the semiconductor device.
In a case where a temperature sensing diode is provided in a semiconductor device, it is normal that a polysilicon layer is formed on an upper surface of a substrate through an insulating layer, and an anode and a cathode are formed in the polysilicon layer. When the temperature sensing diode is applied to a semiconductor device (for example, a semiconductor device using a SiC substrate) that operates under high temperature, highly accurate temperature detection might not be possible due to leak current. In short, in the semiconductor device that works under high temperature, temperature of the polysilicon layer becomes high, and leak current is easily generated. When leak current is generated in a temperature sensing diode that uses a polysilicon layer, highly accurate temperature detection becomes difficult. Therefore, it is considered to form the temperature sensing diode in a semiconductor substrate. This prevents leak current, and temperature detection by the temperature sensing diode becomes possible even under high temperature. Since the temperature sensing diode is formed in the semiconductor substrate, it is possible to arrange the temperature sensing diode in the vicinity of a power semiconductor element, which makes it possible to detect temperature of the power semiconductor element more accurately.
However, when the temperature sensing diode part and the power semiconductor element part are provided in the same semiconductor substrate, a parasitic bipolar transistor might operate. For example, a case is considered where a temperature sensing diode part and an n type MOSFET part are provided in a same semiconductor substrate. In this case, a p type base region is arranged so as to be in contact with an upper surface of an n type drift region. The p type base region is arranged in a range that faces an upper surface of the semiconductor substrate. A p type anode region and an n type cathode region are arranged in the p type base region of the temperature sensing diode part, and an n type source region and a p type contact region are arranged in the p type base region of the n type MOSFET part. As electropositive potential is applied to the anode region of the temperature sensing diode part, electropositive potential is applied to the base region of the temperature sensing diode part. Then, an npn parasitic bipolar transistor, which is structured by the n type cathode region, the p type base region, and the n type drift region, operates. As a result, large current flows to the cathode region, and temperature detection accuracy of the temperature sensing diode might be degraded.